1. Lecture 1 Overview: roadmap 1.1 What is computer network? the Internet? 1.2 Network edge  end systems, access networks, links 1.3 Network core  network structure, circuit switching, packet switching 1.4 Delay, loss and throughput in Internet 1.5 Protocol layers, service models 1.6 Networks under attack: security 1-1

2. Lecture 1 How is the Internet Organized  A hierarchical structure.  hosts combine to form a Local Area Network (LAN).  LANs combine to form an Autonomous System (AS)  Autonomous Systems combine to form the Internet. Internetworked networks – Internet ! 1-2

3. Lecture 1 What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts = end systems  running network apps Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data) 1-3

4. Lecture 1 What’s the Internet: “nuts and bolts” view  protocols control sending, receiving of messages  e.g., TCP, IP, HTTP, Skype, Ethernet etc.  Internet: “network of networks”  public Internet versus private intranet  Internet standards  RFC: Request for comments Home network Institutional network Mobile network Global ISP Regional ISP 1-4

5. Lecture 1 What’s the Internet: an operational view a human protocol and a computer network protocol: human protocol Hi Got the time? 2:00 time 1-5

6. Lecture 1 human protocols: … specific msgs sent … specific actions taken when msgs received, or other events network protocols:  machines rather than humans  all communication activity in Internet governed by protocols What’s the Internet: an operational view 1-6

7. Lecture 1 What’s a protocol? a human protocol and a computer network protocol: Internet protocol example Hi Got the time? 2:00 TCP connection req. TCP connection reply. Get http://jjcweb.jjay.cuny.edu/ssengupta/slide.ppt time human protocol 1-7

8. Lecture 1 human protocols: … specific msgs sent … specific actions taken when msgs received, or other events network protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt What’s the Internet: an operational view 1-8

9. Lecture 1 Take home messages  According to you, what are the three most important physical components of computer network?  Name four Internet applications?  What does a network protocol do? 1-9